Manufacture of niobium by fusion electrolysis



United tates Patent l 3,062,727 MANUFACTURE OF NIOBIUM BY FUSIONELECTROLYSIS Ernst Adalbert Pokorny, London, England, assignor toSociete Generale Metallurgique de Hoboken, Hobokenlez-Anvers, Belgium, alimited company of Belgium No Drawing. Filed Dec. 4, 1959, Ser. No.857,254 Claims priority, application Great Britain Dec. 10, 1958 3Claims. (Cl. 204-64) The electrolysis of niobium with fused electrolytecarried out with electrolytes consisting for instance of the doublefluoride of potassium and niobium in a mixture with alkali fluorides andchlorides presents great dfliculties in that the cathodic deposit of themetal may contain lower oxides of niobium, and in order to obtainmetallic niobium, the electrolytic product has to be substituted to aseparate reduction operation, which is rather uneconomical.

It is already known to use alkali metals as additions to the electrolytein the fusion electrolysis of uranium and other rare metals to preventoxidation of the metal which is deposited on the cathode in powder orsponge form. The alkali metals are not added to the electrolyte as suchbut in the forms of their halides, forming during the electrolysisclouds or a fog of metallic alkali within the electrolyte. The alkalimetals do not form alloys with the uranium.

The present invention applies to niobium and uses as additions stronglyreactive metals, capable of forming an alloy with the niobium, at leastto a certain extent. Such metals are chosen in a class consisting of:calcium, magnesium, aluminium, zinc, and rare earth metals. One orseveral such metals may be used. The additions can be made either in theform of metals, or of their alloys as such, or in the form of those oftheir compounds which are decomposed during the electrolysis. Theadditions may be made either before or during or immediately after theend of the electrolysis.

The electrolyte normally used for the electrolysis of niobium has aspecific gravity of between 2.3 and 2.7 and therefore the mentionedlight metals cannot be easily brought into contact with the niobium inthe electrolytic cell. They may be introduced in the form of theiralloys with the heavier metals, such as zinc and/or the rare earthmetals. It is also possible to add their halides to the electrolyte, themetals being formed by electrolytical decomposition during theelectrolysis of the niobium.

The rare earth metals and their alloys are particularly suitable for thepurpose because of their high density. Furthermore, they are to acertain limited extent absorbed by the niobium, forming an alloy ofimproved Patented Nov. 6, 1962 properties, above all of greaterresistance to oxidation during subsequent manufacture.

The fusion electrolysis of the rare earth metals is effected underworking conditions very similar to those of the fusion electrolysis ofniobium, i.e. at 8-12 volts and at a temperature of about 700-900 C.Therefore, instead of adding the rare earth metals as such to theelectrolysis, they can be added to the electrolyte in the form of theirhalides. The rare earth metals are thus deposited electrolytically onthe cathode at the same time as the nobium and they react with thecathodic deposit of niobium, in order to reduce the oxides to metalform, at the same time becoming alloyed with the niobium and improvingthe properties of the latter in various respects.

This can to a certain extent be achieved also with calcium and/ormagnesium and/or aluminium as such or in the form of their alloys withheavier metals.

The oxygen-containing reaction products of the rare earth metals or theother metals mentioned, with the oxides of niobium are partly dissolvedin the electrolyte, and partly collected at the boundaries between theniobium deposit and the electrolyte. They can be separated from theniobium metal powder by any known chemical method or mechanically by anyknown ore dressing method.

The following approximate quantities of the various metals added maybeused: for each 100 grams niobium oxide introduced in any form into theelectrolyte, an addition of 25.5 g. aluminium is made, or 36 g.magnesium or g. calcium or g. zinc or g. rare earth metals (misch metal)or a proportioned mixture of these metals.

What I claim is:

1. Method for the preparation of metallic niobium which comprisespassing a direct electric current through a fused electrolyte bath of adouble fluoride of niobium and an alkali metal, said bath containing amember selected from the group consisting of a rare earth metal, a rareearth metal alloy, and a rare earth metal halide, and recovering analloy of niobium and rare earth metal.

2. The method of claim 1 in which the bath temperaaure is about 700900C.

3. The method of claim 1 in which the bath contains misch metal.

References Cited in the file of this patent UNITED STATES PATENTS2,777,809 Kolodney Jan. 15, 1957 2,899,369 Slatin Aug. 11, 19592,947,672 Ervin et al. Aug. 2, 1960

1. METHOD FOR THE PREPARATION OF METALLIC NIOBIUM WHICH COMPRISES PASSING A DIRECT ELECTRIC CURRENT THROUGH A FUSED ELECTROLYTE BATH OF A DOUBLE FLUORIDE OF NIOBIUMIUM AND AN ALKALI METAL, SAID BATH CONTAINING A MEMBER SELECTED FROM THE GROUP CONSISTING OF A RARE EARTH METAL, A RARE EARTH METAL ALLOY, AND A RARE EARTH METAL HALIDE, AND RECOVERING AN ALLOY OF NIOBIUM AND RARE EARTH METAL. 